An exposure apparatus which forms a latent image pattern on a photosensitive agent in the following way is available. That is, the exposure apparatus transfers a pattern of an original such as a reticle onto a photosensitive agent applied to a substrate such as a wafer. Alternatively, the exposure apparatus draws or transfers a pattern onto a photosensitive agent on a substrate by a charged-particle beam such as an electron beam. Such an exposure apparatus incorporates a positioning apparatus to align an original and substrate.
FIG. 11 is a plan view schematically showing an example of a positioning apparatus which drives a movable body in one axial direction. A stage 101 as the movable body is guided to be smoothly movable on a stage base 102. The stage 101 is driven by an actuator (not shown) and moves on the stage base 102. As a guide technique, for example, a method using a linear guide which generates friction or a method using hydrostatic air, static air, or static pressure bearing to guide the stage in a noncontact manner is available. If a linear guide is used, the maintenance of the apparatus is periodically necessary for keeping the stage positioning accuracy and guide function in a good state. This structure is unsuitable for an exposure apparatus which requires high accuracy and high productivity. If hydrostatic air, static air, or static pressure bearing is used, the stage can be controlled with high accuracy because this structure generates little friction in a noncontact manner.
The guide method using hydrostatic air, static air, or static pressure bearing generally applies pressurizing force (attraction force) between a stage and a stage base which guides the stage, in order to increase the supporting rigidity by raising the air pressure. As the pressurizing technique, a method using a magnet (magnetic force) or a method using a vacuum negative pressure is available. In general, the method using a magnet is more effective in pressurization than the latter method, and can guide the stage with high accuracy. However, when a magnetic field (a pressurizing magnet placed on the stage) moves on a magnetic body having a low insulation resistance, an eddy current is generated. This disturbs stage driving and heats the stage base. In recent years, the moving speed of the stage is increased to improve the throughput, resulting in an increase in heat amount due to the eddy current.
To solve this problem, there has been known an arrangement to remove heat of a stage base due to an eddy current using a refrigerant. In the example shown in FIG. 11, the refrigerant is supplied to a refrigerant path 104 in the stage base 102 through a refrigerant inlet 103. As the refrigerant passes through the refrigerant path 104, it removes heat and is discharged from a refrigerant outlet 105. For temperature control of the refrigerant, temperature sensors 106 arranged at appropriate portions of the stage base 102 can be used. Alternatively, a temperature sensor which directly measures the temperature of the refrigerant can be used. In most cases, a place of the stage base 102, which most requires suppression of temperature rise, is around the center of the stage base 102. However, the temperature sensor cannot be arranged at that place in most cases, so it takes much time to stabilize the temperature of the entire stage base 102. Moreover, a good response characteristic to a change in stage driving profile or a variation in temperature due to the stop and driving of the stage is not obtained.
FIG. 12 is a plan view schematically showing the arrangement of a twin-stage type positioning apparatus with a plane motor structure. The same reference numerals as in FIG. 11 denote similar constituent elements. This positioning apparatus has two stages which contribute to improvement of the throughput in an exposure process. More specifically, as a alignment measurement process is performed using one of the stages, a wafer having undergone the alignment measurement process is exposed using the other stage.
In general, since the exposure process and the alignment measurement process have different stage driving profiles, they produce different heat amounts due to an eddy current generated in the stage base 102 upon driving the two stages. If such a twin-stage type positioning apparatus has only one cooling system, the temperature distribution may become nonuniform because the heat amount in an exposure process area is different from that in an alignment measurement area. This degrades the measurement accuracy of the stage position. Moreover, the temperature of the wafer varies, resulting in a deterioration in exposure accuracy, particularly, overlay accuracy.